Terrestrial and Solar Limits on Long-Lived Particles in a Dark Sector

TL;DR

This paper explores constraints on long-lived particles in a dark sector from terrestrial and solar experiments, proposing new experimental directions to detect these particles through their unique decay signatures.

Contribution

It provides a comprehensive analysis of existing bounds on dark sector particles' lifetimes and suggests novel experimental approaches for future searches.

Findings

Terrestrial beam-dump experiments constrain lifetimes of 10 cm to 10^8 cm.

Solar observations limit lifetimes up to 10^15 cm.

New experimental strategies are proposed for detecting long-lived dark sector particles.

Abstract

Dark matter charged under a new gauge sector, as motivated by recent data, suggests a rich GeV-scale "dark sector" weakly coupled to the Standard Model by gauge kinetic mixing. The new gauge bosons can decay to Standard Model leptons, but this mode is suppressed if decays into lighter dark sector particles are kinematically allowed. These particles in turn typically have macroscopic decay lifetimes that are constrained by two classes of experiments, which we discuss. Lifetimes of 10 cm < c tau < 10^8 cm are constrained by existing terrestrial beam-dump experiments. If, in addition, dark matter captured in the Sun (or Earth) annihilates into these particles, lifetimes up to 10^15 cm are constrained by solar observations. These bounds span fourteen orders of magnitude in lifetime, but they are not exhaustive. Accordingly, we identify promising new directions for experiments including searches for displaced di-muons in B-factories, studies at high-energy and -intensity proton beam dumps, precision gamma-ray and electronic measurements of the Sun, and milli-charge searches re-analyzed in this new context.